1. Field of the Invention
The present invention relates to an image-forming apparatus, such as an electrographic printer or a copying machine, in which an electrostatic image is formed and then reproduced as a toner image. More particularly, it relates to such an apparatus having a clam-shell type frame structure by which a process cartridge can be easily inserted and removed and a paper jam can be quickly cleared.
2. Description of the Related Arts
FIG. 1 is a schematic side view of an electrographic printer, wherein a process cartridge 2, a transfer-charger 3, and a fuser unit 4 are accommodated in a housing 1. The process cartridge 2 consists of a photoconductive drum 5 around which a developer unit 8, a precharger 7, and a cleaner 9 are arranged. All of these elements are built-in to a case to form a cartridge. A motor M is provided in the housing 1 to drive the photoconductive drum 5, the fuser unit 4, and a plurality of rollers 6a6b for moving a cut sheet 25 through the printer.
In the printing operation, cut sheets 25 are fed one by one from a hopper 10a or 10b, transported into an area between the transfer-charger 3 and the photoconductive drum 5, moved past the fuser unit 4, and finally, discharged to a stacker 12. More specifically, the precharger 7, an LED-array 11, the developer unit 8, the transfer-charger 3, and the cleaner 9 are sequentially arranged around the photoconductive drum 5. Accordingly, during a counter-clockwise rotation of the drum 5, the periphery thereof is uniformly charged by the precharger 7, an electrostatic latent image is then formed on the drum periphery by the LED-array 11 in accordance with input information, the latent image is reproduced as a toner image by the developer unit 8, the toner image is transferred to the surface of the cut sheet 25 by the transfer-charger 3 and fixed thereon by the fuser unit 4. Finally, the cut sheet 25 is discharged as a hard copy to the stacker 12.
As the printing operation is repeated, a powdery toner stored in the developer unit 8 is gradually consumed. When the toner is exhausted, the process cartridge 2 is replaced as a whole by a new cartridge. In the conventional printer, this replacement is carried out, as shown in FIG. 2, by laterally withdrawing the exhausted cartridge in the same direction as the axis of the photoconductive drum through a window 18 formed in the side wall of the housing 1, and inserting a fresh cartridge into the housing 1 in the reverse order, as disclosed in Japanese Examined Pat. Publication Nos. 58-54392 and 61-48152.
The structure of the housing 1 of the above printer, however, is weakened by the provision of the window 18, and this problem becomes more serious if the printer is small in size. In addition, space must be provided outside the side wall of the apparatus, to enable the lateral withdrawal and insertion of the process cartridge 2.